4 TERJEMAHAN -4- [ZCT 304El UNIVERSITI SATNS MALAYSIA Third Semester Examination 2002/2003 Academic Session April 2003 ZCT 304E/3 - Electricity and Magnetism I1 Time : 3hours Please check that the examination paper consists of TWELVE printed pages before you commence this examination. Answer all FIVE questions. Students are allowed to answer all questions in English OR bahasa Malaysia OR combinations of both. 1. (a) A circular disk of radius R has a uniform sufface charge density cr. Find the electricd field at a point on the axis of the disk at a distance z fiom the plane of the disk. (8/20) (b) A right circular cylinder of radius R and height L is oriented along the z - axis. It has a nonuniform volume density of charge given by p(z) = p, + pz with reference to an origin at the center of the cylinder. Find the force on a point charge q placed at the center of the cylinder. ('hint: use the answer obtained fiom part (a)) (12/20) 2. A charge q is distributed uniformly throughout a non-conducting spherical volume ofradius R. (a) Show that the potential a distance Y fiom the center, where Y < R is given by 4(3R2 -r2) V= (15/20) 8m,R3 (b) What is the potential at a point Y > R? (5120)

5 -5- [ET 304E] 3. Two concentric, spherical, conducting shells of radii r1 and r2 are maintained at potentials q+ and <p2 respectively. The region between the shells is filled with a dielectric medium. (a) Show by direct calculation that the energy stored in the dielectric is equal to C(% -%)2 (5/20) 2 (b) Determine C, the capacitance of the system. (15/20) 4. A long coaxial c a ~ e ~ - o ~ i s t s _ o f ~ o ~ shown below. There are equal and opposite currents i in the conductors. Determine the magnetic field B at r if (b) a<r<b, (5/20) (c) b<r<cand (5/20) (d) I > c (outside the cable) (Y20)..6/-

6 -6- [ZCT 304Ej 5. Show that the magnetic vector potential for two long, straight, parallel wires carrying the same current, I in opposite directions is given by where r2 and ri are the distances from the field point to the wires, and fi is a unit vector parallel to the wires. (20/20)... 7/-

Section A [28 marks / markah] Answer all question Jawab semua soalan 1. A student carries out an experiment to study the relationship between the velocity of trolley, v and the height of the trolley on